Hello everybody!
I've been trying to animate the parameters for the particles size on Trapcode Particular.
What I did was write a word using the particles for a smoke/cloud effect. Now I want the particles forming this word to increase their size to become a single cloud of smoke.
Sorry for my english, i hope i could make myself clear.
Can somebody help me?
Thanks!

You can't keyframe the particle size of existing particles directly. Particular's Particle Size property controls the size of particles at their birth -- it does not affect the size of particles after they are born.

If you want to change the size of existing particles over time, you can draw a shape in the "Size Over Life" graph. Time is on the x (horizontal) axis; size is on the y (vertical) axis -- so you want the graph to go up as it goes right. There are some built-in graphs you can click on.

Form is another particle system from Trapcode. Unlike Particular, which is a particle emitter, Form is a particle array system. In Form, you don't have control over the emission of particles; there are a fixed number of particles in the system that does not change with time. However, unlike Particular, Form allows you to directly animate particle properties over time, or according to layer maps. It's a different approach, which different strengths and weaknesses, but it may be more in line with what you're thinking here.